What is coral bleaching and why is it harmful?

Coral on the Great Barrier Reef recently began spawning, but will bleaching still have impact these species?
07 December 2021


Coral reef & a fish



What is bleaching? Why is it bad for coral? And why is the ocean so colourful?


Julia Ravey spoke to deep-sea explorer Diva Amon about what impact coral bleaching could have on our ocean ecosystems...

Diva - Corals are very sensitive to temperature and of course, corals are animals, right? Let's start there. And so a lot of them have a symbiont, which is fundamental to keeping them alive. And when they get very, very hot that symbiont can die. And once that happens, the coral will begin to lose its tissue and die and go white. Sometimes coral can be bleached and not fully die and it can come back, but often it's much reduced from what it was. And that's really bad of course, because corals are like this three-dimensional structure that is basically a home, a shelter, it's such a key part of our shallow waters ecosystems and our coral reef ecosystems that to lose them would just be absolutely awful. And it's thought that we may lose them by 2050, if we continue on this trajectory that we currently are with global temperatures warming. In terms of why is ocean life so colourful, there's so many different reasons, but I'd like to sort of tweak the question a little bit and say, ask why is deep sea life colourful? Because that actually doesn't make sense because you're living in the dark. So why do you need colour? And actually a lot of life in the deep ocean can be red or purple or mauve. And the reason for that is that as you go deeper in the ocean, your light not only becomes less, but you actually lose wavelengths of light. And the first wavelength of light to be lost is red. And so that means that you actually can't see red from very, very shallow as you go deeper. That's why the ocean looks blue because blue is one of the last wavelengths to be left. And so if you're red in the deep sea, because there's no red light down there, or white lights that matter, it means that you're basically wearing an invisibility cloak. And so all of these animals are sort of shrouded in darkness. And then there are a lot of other animals that are white, that are black, that are yellow. I mean, really it confounds you as to what, how and why there is so much color down in the deep sea. And one of the other main reasons is that actually the color has nothing to do with being seen. The color is just a byproduct of something else going on. So it doesn't mean to be yellow. It doesn't mean to be purple. It just is that way because of something else within their body.

Julia - So beautiful to look out, I'm very jealous you get to look at it on a very regular basis.


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